Stop mechanism for step-by-step plungers



Feb. 10, 1953 H. s. AUSTIN 2,627,757

STOP MECHANISM FOR STEP-BY-STEP PLUNGERS Filed May 10, 1949 INVENTOR 14F440 J? z4fiJ77/V.

0 Z TTORNEYS ticularly,

Patented Feb. 10, 1953 UNITED STATES PATENT OFFICE STOP MECHAWISM FOR STEP-BY-STEP PLUNGERS Harold S. Austin, Dallas, Tex.

Application May 10, 1949, Serial No. 92,484

10 Claims.

- l The present invention relates to stop mechanisms for step-by-step plungers and, more parto such structure of hypodermic syringes, and constitutes an improvement over such structure as shown in my U. S. Letters Patform of cam operated parts so constructed and arranged as to assure compactness and to permit use of circular housing structure requiring a minimum Of machining and well adapted to economical mass production.

A further object of the present invention is the provision of structural embodiments of such stop mechanism which are readily constructed and allow emcient use and operation thereof.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combination of elements and arrangement of parts, which will be exemplified in the construction hereinafter set forth, and

the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing, in which:

Fig. 1 is an exploded perspective, with parts broken away, of a hypodermic syringe embodiment of the present invention, showing the parts of the stop mechanism as viewed from above;

Fig. 2 is a top plan view of certain parts of the hub assembly of the structure shown in Fig. l, with the plunger shaft shown in section and the control lever or manual button swung to the left to permit the stop on the left side to be biased toward stop-engaging position of that shaft;

Fig. 3 is a View similar to Fig. 2, with parts broken away, showing the stop on the left side snapped. into engaging position with respect to the shaft as the latter is pushed inward or downward to discharge a dosage of predetermined amount;

Fig. 4 is a view similar to Fig. 3, showing the control lever moved to a central neutral position during its swing over to the right side;

Fig. 5 is a view similar to Figs. 3 and 4 showing the control lever swung to the right side to permit the right hand stop to assume a position similar to the position of the left hand stop, as shown in Fig. 2;

Fig. 6 is a view similar to Fig. 4 of a modified form of the structure shown therein, simplified for commercial production; and

Fig. '7 is a top plan view similar to Figs. 2 to 5 inclusive of another embodiment of the present invention more nearly similar to thestructure shown in Fig. '7 of my above identified patent with respect to the housing construction.

Referring to the drawing, like numerals identify similar parts throughout. As willbe seen from Figs. 1 to 5 inclusive, a preferred embodiment of the present invention comprises a hub assembly I!) adapted to be mounted on the toip end of a casing barrel structure (not shown) which may be similar to that described in my above identified patent. The hub assembly [0 preferably includes a cylindrical base member II, to the bottom end of which is preferably secured a pair of diametrically-opposed, laterally extending wings I2, I2 to serve as finger grips.

The top end of the cylindrical member II is preferably counterbored to provide a socket I3 therein having a flat bottom I4 and a circular side Wall I5, with the latter notched at I6 to provide for projection therefrom of the control lever or thumb button. concentrically of the socket I3, the cylindrical base member II is provided with a circular hole I! reciprocatively to receive therethrough a circular plunger shaft I8.

The plunger shaft I8 has a plurality of longitudinally-extending series of abutment means to cooperate with stop means housed in the socket I3 of the hub base member I I, and for this purpose preferably is provided with a plurality of pairs of such series of such abutment means, preferably in the form of notches. A cooperative pair thereof preferably isarranged along the shaft I 8 on diametrically opposite sides as indicated respectively at I9 and 20, with those in one series staggered with respect to those in the other series. Each of the notches I9-I9 and. 20-40 has an upwardly and inwardly sloping face 2| on the bottom side thereof to permit stop means readily to slide thereinto, and a substantially fiat, transversely-extendin top face 22 to provide the stop abutment engageable against the stop means when snapped into any one of those notches, so as to limit and stop movement of the plunger shaft. Thus, the distance longitudinally of the shaft I8 between abutment face 22 of one notch l9 and abutment face 22 of the next succeeding diametrically-located notch 20 predetermines the length of longitudinal shaft movement during one step of motion thereof. The length of the next step of motion of the plunger shaft, of course, is predetermined by thelongitudinal distance along the shaft i8 between abutment face 22 of that latter notch 26 and the abutment face 22 of the next succeedin notch l9. As previously made clear in this art, more particularly by reference to my above identified patent, such plunger shaft means preferably is also provided with two other opposed. series of notches spaced different distances apart along the plunger shaft I8 so as to permit delivery from the hypodermic syringe of dosages of different predetermined amounts. There is shown at 23 a notch of one of those latter series of abutment means.

The plunger shaft mechanism which is housed in the socket 13 of hub base member H prefably comprises an opposed pair of stop members 24, .24, each preferably in the form of a pivotally mounted lever of the second class. Each of the two stop levers 24, 24 preferably has its butt end 25 thereof provided with a hole in which is seated a screw 26 threadably engaged in an internallythreaded socket in the bottom I4 of the housing socket I 3 for pivotal mount of that stop lever. The other end of each cam lever 24 is provided with a cam follower 2'! having a curved face 28 on its inner side terminating at its root in a .notch 29. Between the notch 29 and the pivoted butt end 25, each lever 24 is provided with an abutment-engaging portion 30, which is preferably in the form of a blade, as shown, so as readily to snap into any of the notches on the shaft l8.

Between the cam followers .21, 21 is pivotally mounted an operating cam member 3| which preferably i in the form of a lever pivotally mounted by a screw 32 to the bottom 14 of housing socket I3 opposite the notch IE in the socket side wall [5. Cam lever 31 has a fan-shaped portion 33 terminating at its sides in radial projections 34, 34, hereinafter called nodes with an arcuate surface 35 extending therebetween and preferably formed along the arc of a circle circumscribed about pivot screw 32. Cam lever 3i also has behind each node 34 a cam followerreceiving notch 33. An operating lever arm 37 is fixed to cam lever 3|, extends out through the slot l5, and carries a thumb-engaging projection or button 38, so that the cam lever may be flipped back and forth about its pivoting center 32 with application of pressure to opposite sides of the button.

The abutment-engagin portions 38, 3c of the stop levers 24, 24 are biased inwardly toward each other, and thus toward shaft 38 arranged therebetween, by any suitable resilient biasing means. i

In the embodiment shown in Figs. 1 to inclusive, such resilient biasing means preferably comprises a cam spring member 39 in the form of a C- shaped piece of steel wire seated within the housing socket l3 beyond the butt ends 25, 25 of the stop levers and with the two end 41!, 49 thereof brought up to and curved or bent inwardly to seat in holes in the outer sides of the stop levers in the vicinity of the cam followers 21, 21 thereof. Consequently, those cam followers 21, 2'! are biased inwardly toward each other and the cam lever 3| interposed therebetween.

As shown in Fig. 1, a cover plate member 31, preferably cylindrical in shape, is provided with its lower end rabbeted to form a cylindrical projection 42 to seat within the socket flange 15, so as to close off the top of the socket for securely housing within the latter the stop mechanism previously described. Cover plate 4| has a hole 43 coaxially extending therethrough for alignment with the hole I? in the hub base member I I, reciprocatively to receive the plunger shaft I8. To one side of the hole 43 in cover plate 4! is provided a hole within which is rotatably mounted a screw id adapted threadably to be received in an internally-threaded socket 45 in the bottom Id of housing socket 83, so as removably to secure the cover plate to the hub base member H in properly oriented position. Cover plate M is ccunterbored on the top side thereof to provide a shallow recess 36, and within that recess there are provided two radially-spaced, internallythreaded holes 41 and 48 for a purpose to be explained later.

The hub assembly it is completed by a circular cap plate 1. .9 having an axial hole 5% extending therethrough for alignment with shaft holes I? and d3 cooperatively to receive the plunger shaft for reciprccative motion. Circular cap plate 49 is adapted to be seated within the recess 46 in cover plate ti. Cap plate 59 has a radial projection ti on the inner wall of its axial hole 58 to be slidably received in a longitudinally-extending groove 52 formed in a side of shaft l8, to prevent relative rotation between the shaft and the cap plate. The latter also has a hole to one side of its axial shaft hole in which is rotatably mounted an indexing pin 53 having a lower externally-threaded end 5 extending therebelow. The latter is adapted to selective threaded engagement into either of the two internally-threaded holes and as in top plate ii, so that plunger shaft 18 may be rotated between and selectively fixed in two positions as are determined by that cooperative engagement so as properly to orient the abutment notches on the shaft with respect to the stop mechanism housed in the socket $3.

With the parts of the embodiment of the device shown in Figs. 1 to 5 inclusive properly assembled; with the stop mechanism housed in socket l3 beneath cover plate *2! secured to hub base member I i by screw 3 5, and with cap plate 39 temporarily secured to the cover plate by engagement of index bolt 43 in hole 41 to predetermine delivery of successive dosages of an amount, for example, of about two cubic centimeters (2 cc.); the operation of the device is as follows, as will be more apparent by reference to Figs. 2 to 5 inclusive. The engagement of index bolt 53 in hole M aligns the two cubic centimeters (2 cc.) notches I9|9 and 2l20 respectively with the opposed stop blades 30, 30 of stop levers 24, 2%. If the cam 3! is swung to the right to the position indicated in Fig. 2 by pressing the thumb button 38 to the left, the stop lever 24 on the left side will be biased by spring 39 toward the shaft 13 so that the curved surface of the latter between those notches i9, 19 will be engaged by that levers stop blade It will be noted from Fig. 2 that the left cam projection or node 33 will be located opposite the notch 29 in stop lever 2d, and the cam follower 2? thereof will be located opposite the notch 36 in the cam lever 31, with that stop lever held free from contact with the cam by contact of its stop blade 36 with the adjacent curved surface of shaft l8.

Upon depression of the plunger shaft l8 in the usual manner of discharging a dosage for subcutaneous injection, the nearest notch 19 will be brought down opposite stop lever blade 39 so that the latter will slide up along the sloping face 2! eventually to be engaged beneath transverse stop face 22 to determine the length of the injecaezms'r tion-r stroke. --Asstop blad tfl snaps into notch 19 in that mannery that left' han'd stop lever "-26 havingbiased'motionin toward the axis of shaftiS, cam-notch-Sfireceives cam follower 21 I and stop lever notch' 29 receives camnode t as shown in-Fig. 3. In the meantime, the arcuate -cam-surface 35,-engages' the cam follower-surface '28 of theother stop lever i'andslid'es therealong to holdthe stop'blaele' 33 of'the latter "free from contact with shaft! 8.

"In'order to free stop blade 30 of left 'hand'stop lever 2 outof notch "IS, "the cam 3| is then to be-swung over to the other side by flipping cam operatingbuttonor projection 38 to the right. During-this swingingaction of-cam 3i, "thelatter'willbe moved-toand eventually through a centralrneutral position; such as that shown "in Fig. 4. In" that position, "the cam-=nodes34, "3:3 ;contact:the 'curved'faces 28. 28 "of the cam "followers 21; Z'Ijefiectivelyto hold the stop levers "24; 24 in 'spread=apart positions shown in Fig. 4,Wlth theinstopblades '30; 3t!- both free from .contactwith the si'des'of plunger shaftl 8. Then, as the operating-lever isthrownfurtherto the right'to the position-shown inJFig; 5,-toswing cam 3| to the left to'theother'extremepf its path of traveljthlefttcani node snaps past "the end of camfollower 21 'of' the'l'eftstop' lever 2 tto bringiface .28 of "that camfoll-owerinto contact with thearcuatefcam surface 35 :tohold stop blade tiliiof .that i'left "stop 'lever'out "of contact withthe: side; ofiplun'ger shaft I 8. "This action, of course; isfacc'ompaniedmy' rotation of the right cam node 36 inwardtawaytfromithe 7 past face v28 ofcam'lollowerZT of'the'right 2817013 lever 24 to'lthe position shownin'Fig; so

.that the stop bladett thereof :willbe biased to contact with theside ofthe plunger shaft It.

With' downward thrust .of the plunger shaft [8 thereafter, to discharge the next dosage, notch .26 .is brought to receptiverelation with respect .to stop blade .36 of theright stop lever' 24.. in a. manner similar to the previously described .ac- .tion .of .the left stop .lever 14' with respect to :notch 19. .As a result, stop..blade"3ll of the right stopleveri is eventually engaged by the transverse top. facef22 .of notch ZQ to stop further downward motion ofshaftl8, with notch'lZS in right hand stop lever 24 receivinglthelrightcam .node 34, and with the. right notchjtfiin the cam lever 3! receiving .theicam vfollower. .21 on .that

. .cam. lever, as. the. latter is .biased.inwarditoistop or abutmenteengaging .pos'ition. .sIt will .he seen ;.thatwith flipoithe operating-or control .proj ection or button 38 back to theuleft position,.as ashowninFig. 2, the :sequence .of ..-operational steps :previously describedislrepeated.

It i .tov be understood that, although it.is. pre- .:ferred-cam lever 3! inits central neutral position shown in Fig. 4 so spreadsapart the stop le-' --vers 24, 24 as to hold their stop blades .30,=30 free from contact with thecurved sidesof theplunger shaft 13, not only to assure completev freeing of those stop blades alternatel from the-notches I9l 9 and 20.2il-, butalso to permit free recipro -to'=permit theedges of the-stop blades'tfl, 36 to 'passibeyond isuchilchamferedcdgesrmitht'theLlatter further :cammingmhose sstop 'leversmutwatdly during plunger. depression..ltlrr'suchzmechanism, 'of coursa ithe alternate:camming:o.ut of;.=the:stop 5 levers-24, 24 is:accomplishedjmaumannen'similar to that described :above', but :lthescentralineutral position of'cam i3 lwill'inotrholdltheistop blades 30, 3 0 out: of :contact :withfflw curved-1 sides ofi the shaft l 8. .In fact;itheyozvillstride.tin'rbiasedazcon- 10 tact with "the. curvedl'sidesrof the shaftzuntiltthey successively .rare .t-approached :ialternately .zby .notches l 9:.and420, zwhichuwillzpermit :flrst: one and .th eni the otherito move.slightlyinitowardreceivedposition. 5. However, cam 3 l wilhlimits such inwardmotion sotthat the'rstop .blEdeJfirOiaBithGl' :stop lever. 2 4- twill. not' move inwardly. beyond'l the chamferedtedge ofmthel'transversei'top. face 22s-to :efiect :an actual stoppage: of longitudinaltishaf t motion. Actually,:.the:rshaf.t 18min: su'ch-avaried 2() stop .me'chanismstructure .may rbe reciprocated back and forth with a slight successive clicking noise when: cam. 3 I :is;in". the: central neutral .posi- ;tion shown in Fig.4.

In. the .event that. dosages :in', quantities Jdilf'er- 5 ent from those dictatedby notches |9-l 9::an'd 20-20 are desired, it. is'merely .necessaryifor the operator tounthreadtheilower. end 5410f in- .dex .bolt 53 "out of internally-threaded.r'hole- 41 in the cover. plate-:4 I? and then to'rotate cap iplaite =49 counterclockwise :I'toIbringLthat .index boltito engaging position withtrespect to Iinternallythreaded hole 48. This, of course, rotates plunger shaft l8 .by virtuettofithe'zintersengagement of pro- -j'ection 5 if on-rcap plate :49kwithxtheglongitudinal groove. 52. in :thessideroftshaft :I 8;:sozas to arrange the other series -:of' notchesz23- 43 oppo'site' the stop .levers 24,; 24 to =bringzabout cooperation -therebetween: in :aiimanner similarto 'lthat describedcabove connection: .with the -two- 'series A 1 somewhat :simpler :construction than that eshownzinfligs- 1'; 00:5 inclusivegis shown Fig.6,

- which mayi'belmoredesirable for economicttlmass aproduction. :The chief diiferences -will be foufid in ::the stoplevers and -their-operating oam.

Each stopv lever lzd ispas shownyof quite simple design requiring-a minimum ofmachining. The inner corner tZ'T of the freeend of each stop J lever I24 constitutes the 0am follower adapted toride against the =arcuate endsurface 435- 'of cam-t portion 4 33 formingone end -of cam-lever .131. Each stop lever [2 1iis-preferablyprovided .IOI'I. its inner edge 430a near-its freeend witha notch l2 9;: and thate'dge-may =be sharpened inr," ward of-that notch opposite 'plunger shaft -l 8 by chamfering the underside thereof 'to' facilitate .snappinginto the 'shaftmot'ches.

The cam lever i I 3| of-the Figg '6"st'ructureis shaped portion 4-33 has -arcuateend'surface" r35 *thereot terminating in-"r-iodes at I34, I *3 4' at both ends where surfaces ofopposed side-notches or out backs 136, 1-36 join therewith. Notches1'36, J35 alternately'provide clearance "for the stop lever followers I21, l2-1-so that"the-'stop--1evers alternately can be' moved' inward-bybiasingao- "tion of commonspring 39 to abutmenteengaging positionswith' snap into shaft notches. v

' Obviously the action of *the- Fig. 6 structure is quite similar to thatof the Figs; l 'to-5, inclusive, construction, with swing of cam lever 1'3 I .back' and forth i when thumb button38 is flipped to and fro. The followerifl of 'one stop "lever I24 on one side will rideup' outer side 'carn'not'ch 3 6, over node -'i 34- 'and-onto arcuate'cam surface I35 as thumb button 38 is swung to the opposite side. This moves the engaging edge Kit of that stop lever away from plunger shaft it and holds it is such non-engaging position. At the same time the other node 13 is swung inward away from the other stop lever 124 to permit its follower !2! to move into the other cam side notch I36 with biased inward motion of that stop levers edge I39 to engagement of the plunger shaft :2, so that the latter lever edge may snap into a stop notch in the side of the shaft as the latter is pushed inward to discharge a dosage. Flip back of thump button 38, of course, reverses that action, and plunger shaft IB is thus permitted only step-by-step motion as described above, with first one stop lever I24 being permitted to snap into one of the shaft notches 2S and then the other stop lever being permitted to snap into one of the other shaft notches it as the first is backed or cammed away and the plunger is pushed inward.

A further advantage is provided by the Fig. 6 structure in that with cam lever i3! swung to its central neutral position, shown therein, its two node 83 i, 232 snap into the opposed notches (29, l29 more securely to hold the parts in such neutral positions with both stop levers i2 5, 52 3 held outward away from engagement in notches in plunger shaft l8, so that the latter can be freely reciprocated either to fill the barrel or discharge all of the contents of the latter in one stroke.

In Fig. '7 is shown a further modified form of the stop mechanism of the present invention more readily adapted to installation in a hypodermic syringe structure of the type disclosed in my above identified patent. In fact, the housing of the present Fig. 7 structure is generally similar to that shown in Fig. '7 of that patent with a substitution, however, of an embodiment of the cam-operated stop means of the present invention for the toggle-operated stop means of the patented structure. Thus, the bottom of the enclosing casing constituting a part of the hub assembly comprises the opposed finger-engaging wings l2! and I22, having therein elongated chamber or recess 30 in which is seated an embodiment of the stop mechanism of the present invention. As shown in Fig. 7, the stop levers may be of a somewhat modified form, each comprising an elongated member 224 having a curved cam follower 22? and an extending back end 55 intermediate of which a screw 226 may pivotally mount the same in the bottom of the recess formed in hub assembly base E22. Each stop lever 224 carries between its fulcrum point at screw 22% and its cam follower 22'! stop blade 232 for cooperating engagement in the plunger shaft notches. In such an embodiment, the operating cam may also be of modified form, such as that shown at 231, having an arcuate oamming surface 235 extending between side notches 232, 236, the corners 234, 234 at the laterally spaced junctions of that surface with those notches constituting the nodes. Cam lever 23! is pivotally mounted by a screw 232 in the bottom of recess [30. The back end of pivotally mounted cam lever 23! is provided with an arcuate rack 55 meshed with a spur idler 51 rotatably supported at 58 by a pin on hub assembly base 29. Spur idler 53' is in turn meshed with arcuate rack 59 on one end of operating lever 492 pivotally mounted at 60 to hub assembly base 120. An operating arm I53 extends from the opposite end of lever I90 through a slot in the end of finger wing I22 and terminates in a thumb button for back and forth swinging motion.

The stop levers 224, 224 have their cam followers 227, 227 biased toward each other by a common helical spring 239 located between the back lever extensions 55, 55. Thus, during cam operation of each stop lever 224, it acts as a lever of the second class with its working stop blade 22% mounted between the fulcrum point at 226 and the power applying point at cam follower 22?. But, as cam surface 235 is freed from contact with cam follower 227 of one of the stop levers 224 with swing of the cam 23! to a position such as that shown in Fig. 7, so that that follower may pass beyond the near corner node to drop into cam notch 23$, the biasing force of spring 239 causes that stop lever to move to abutment-engaging position to snap its blade into a notch in the side of the plunger shaft. During such biased motion, the stop lever 224, freed from contact with its operating cam 23!, acts as a lever of the first class, with its fulcrum point at screw 226 located between the power application on extension 55 and its work point at blade 230.

The positions of the parts of the embodiments of the stop mechanism shown in Fig. '7 are similar to the positions of the parts of the embodiments shown in Figs. 1 to 5 inclusive, as illustrated in Fig. 5, but at a time somewhat later following indexing of blade 230 of the upper stop lever 224 into notch 20 of plunger shaft 18. In order to free stop blade 23% of upper lever 224 from one of the notches 20 of plunger shaft I8, the thumb button I25 will be swung over to the other side so that lever rack 59 will rotate spur idler 5'? in a counterclockwise direction to swing cam rack 56 in a clockwise direction. As a result, cam 236 will swing up to engage upper lever cam follower 22?, push it out of upper cam notch 236 over the adjacent corner node, and cause cam surface 235 to ride thereagainst, while holding stop blade 23%) of that stop lever out of the path of notch 28 on shaft 18. At the same time, the other lower stop lever cam follower 221 is freed from cam surface 235 past the other corner node, with the other lower cam notch 23% permitting it to move upwardly, so that stop blade 2-30 of the lower stop lever 224 will be swung up into the path of a shaft notch l9 under the biasing influence of spring 239. Thus, by the swing of the thumb button I25 back and forth, the plunger shaft is permitted successively to move inwardly step-by-step to deliver successive dosages in predetermined amounts similar to the action of the embodiments of Figs. 1 to 5 inclusive, and Fig. 6, as described above.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efhciently attained and, since certain changes may be made in the above construction and different embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, nd all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. Stop mechanism for step-by-step plungers comprising, in combination, means for guiding along a longitudinal path a reciprocable plunger means having two series of spaced abutment means arranged longitudinally thereof, a pair of opposed pivoted levers located on opposite sides of the path, each lever having an abutment-engaging portion located alongside of the path for successive engagement of the abutment means of one of the two of said series thereof, resilient biasing means biasing said levers toward each other, said levers having opposed cam followers, movable cam means for alternate engagement of said followers with back and forth cam means motions selectively and alternately to move said levers away from said path and to permit them to move theretoward to provide alternate engaging and releasing action of said abutment-engaging portions relative to their respective series of spaced abutment means, and manual operating means to move said cam means back and forth.

2. The stop mechanism as defined in claim 1 characterized by the provision of said resilent biasing means in the form of spring means tending to move said abutment-engaging portions inward toward the path with such biased motion being alternately opposed by cam manipulation.

3. The stop mechanism as defined in claim 2 characterized by. the provision of said levers each as a member having a cam follower in the vicinity of one end thereof and a fulcrum mount longitudinally spaced from said follower with said abutment-engaging portion located therebetween.

4. The stop mechanism as defined in claim 1 characterized by the provision of said spring means as a single element engaging both of said stop levers and applying the biasing action to both to tend to move them toward each other.

5. The stop mechanism as defined in claim 4 characterized by the provision of said cam as a pivoted lever having a cam portion located between opposed ends of said stop levers of such dimensions and shape as to hold both of said stop levers simultaneously in non-engaging positions when said cam is in a neutral mid-position and to maintain one stop lever in such position when said cam is swung to one side with simultaneous release of the other stop lever, re-

versal of that action being had when said cam is swung to the other side.

6. The stop mechanism as defined in claim 5 characterized by the provision of said operating means as a manual lever connected to said cam lever.

7. Stop mechanism for step-by-step plungers comprising, in combination, means for guiding along a longitudinal path a reciprocable plunger shaft means having two series of spaced abutment means arranged longitudinally thereof, a pair of opposed levers of the second class havmg opposed cam followers at opposed ends thereof, means pivotally mounting said levers along opposite sides of the path at fulcrum points longitudinally spaced from said followers, each lever having an abutment-engaging portion 1ocated between its follower and its fulcrum point for successive engagement of the abutment means of one of the two of said series thereof, resilient biasing means biasing said levers toward each other, and a pivoted cam lever having a fan-shaped portion located between said opposed followers and adapted to be swung back and forth, said fan-shaped cam portion terminating at the sides in laterally spaced nodes to spread said followers apart and having an arcuate surface extending between said nodes against which said followers are adapted alternately to ride with back and forth cam lever swing, said cam lever having notches behind said nodes with each adapted to receive one follower as the other rides against said arcuate surface so that the engaging portion associated with the received follower is permitted to be biased against the side of said plunger shaft means and the engaging portion associated with the riding follower is held away from contact with said shaft means, said nodes being adapted to ride between said followers to spread them apart to non-engaging positions of said shaft means.

8. The stop mechanism as defined in claim 7 characterized by the provision of-opposed notches in said stop levers in the vicinity of their followers simultaneously to receive said nodes as said cam lever is swung to a mid neutral position to hold the parts in positions of nonengagement of said shaft means.

9. The stop mechanism as defined in claim 8 characterized by a common spring resiliently biasing said stop lever followers toward each other.

10. The stop mechanism as defined in claim 9 characterized by a thumb engaging projection mounted on said cam lever and projecting out radially therefrom to an engaging position to permit said cam lever to be swung back and forth thereby.

HAROLD S. AUSTIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 191,087 Wells May 22, 1877 844,356 Hegerhorst Feb, 19, 1907 2,107,568 Haist Feb. 8, 1938 2,289,137 Matter July 7, 1942 2,409,656 Austin Oct. 22, 1946 2,436,750 Gray Feb. 24, 1948 2,457,859 Austin Jan. 4, 1949 

